Around emotional responses the "strenght" in b&w photography is a sort of translation of color way. theory of light and frequencies and so. Maybe the interesting thing is the the way our brain take to compensate that no information we see in b&w..He see color all the time!
I think there are times when a color photograph would be more effective for example to capture a season, as you have yourself said an autumn tree will look more attractive in color as compared to black and white. On the other hand sometimes expressions on a person's face are much better expressed in black and white, Sometimes when you see a black and white portrait you can say for sure that it would have not been that impressive in black and white.
It really helps with fixing chromatic aberrations. I have come across hopeless situations too....where the leaves turned purple and teeth turned green. That's where monochrome saves the day. Tell me of a bride who wants partially purple and partially green teeth associated with the good memories! (that's the sort of lens compact cameras have)
And I remember someone saying that "wedding function...that very moment of happiness usually becomes ancient history very quickly. That is why people love wedding photos to be black and white." and he was an experienced wedding photographer. haha! I'm 18, I can't agree or disagree with him. I'll have to wait for the time being.
I prefer a colorful portfolio though. And yeah, black and white can be used as an intermediate stage for further post processing. Especially when you cannot do drastic color changes. For example, if you make a photo black and white and then create a new layer above it and paint on it and set the layer to "overlay" mode, you can actually color the scene in any way you want to. If you want to change a model's nail paint from red to blue...it is best done after converting that specific region to B&W and then applying blue. Using color balance or hue/saturation from drastic changes sometimes creates serious noise or layering of gradients.
Would a buyer believe the following photo had a dull grey sky originally? I converted it to B&W and used the above method. The sky gradient was copied from an older, better sky image.
55-250mm standard lenses. Dual tube macro flash and external speedlit...